1. Field of the Invention
The present invention relates to a failure diagnosis apparatus for diagnosing failure of an evaporative fuel processing system which temporarily stores evaporative fuel generated in a fuel tank and supplies the stored evaporative fuel to an internal combustion engine.
2. Description of the Related Art
A failure diagnosis apparatus which determines whether there is a leak in an evaporative fuel processing system after stoppage of the internal combustion engine is disclosed, for example, in Japanese Patent Laid-open No. 2002-357164. According to the conventional failure diagnosis apparatus, air is pressurized by a motor pump and introduced into the evaporative fuel processing system, and a determination is made based on a value of the load current of the motor pump as to whether there is a leak in the evaporative fuel processing system. Specifically, when a leak is determined to be present in the evaporative fuel processing system, the load current value of the motor pump decreases. Therefore, when the load current value during the pressurization is lower than a predetermined determination threshold value, a determination is made that there is a leak in the evaporative fuel processing system.
In the conventional failure diagnosis apparatus described above, use of a motor pump is necessary to perform the pressurization, which makes configuration of the apparatus complicated and increases the cost of the apparatus. Further, if there is a leak, another problem with the conventional failure diagnosis apparatus is that the evaporative fuel in the evaporative fuel processing system is emitted to the atmosphere by the pressurized air.